The increase of resistance against β-lactam antibiotics, such as penicillins and kefalosporins, present treatment problems of infections caused by Gram negative rods. Therefore, more and more often β-lactam antibiotics must be replaced with broad-spectrum antibiotics.
Carbapenems represent an important broad-spectrum antibiotic group for treating difficult hospital infections. Carbapenems are typically effective against most aerobic Gram positive and Gram negative bacteria and also against anaerobes. Often used carbapenems are imipenem, meropenem and ertapenem. Bacterial strains resistant against these pharmaceuticals appear in hospital patients particularly in Greece, Israel, United States, Turkey and Far East (China) and in Central America.
Typical bacteria with reduced carbapenem susceptibility are E. coli, Klebsiella sp. and other Enterobacteriaceae sp. In addition, Pseudomonas aeruginosa, and its closely related species from environmental origin, and Acinetobacterium sp. occurring in patients with compromised immune response, often have reduced carbapenem susceptibility. More specifically clinically relevant pathogens may be E. coli; Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii, and there is often no proper antibiotic treatment available due to multi resistant overall phenotype of these super bacteria. Traditional biochemical methods are slow and unspecific and thus early detection of these strains requires new molecular methods.
The reduced susceptibility to carbapenem actibiotics may be caused by one or more of hundreds different β-lactam antibiotic resistance genes combined with changes in cell wall permeability (e.g. specific porine changes) and/or active efflux-associated with hyperproduction of ampC β-lactamases. Typically this causes reduction of carbapenem susceptibility, which is often reversible, and ends when the antibiotic treatment is finished. The reason for this is that the maintenance of the mechanism is energy consuming to the bacterium and disadvantage for its nutrient supply.
Another and more serious reason for carbapenem resistance is enzymes degrading carbapenem antibiotics, so called carbapenemases. In the presence of carbapenemases the bacterium does not need to offer significantly its capability for competition compared with wild type bacteria. Therefore, carbapenemases may alone be the reason for remarkable carbapenem resistance. This mechanism may appear combined to the earlier mentioned mechanisms, which increases the reduction of the susceptibility and consequently the resistance. Carbapenemase genes may be present both in chromosomes and in plasmids. In particular those located in plasmids, are easily transferred to other bacterial species, similarly as those in extended spectrum β-lactamase (ESBL) strains. Strains producing carbapenemase are often also ESBL-strains. Especially, Klebsiella pneumoniae carbapenemases (KPC)- and Verona imipenemase (VIM)-gene family are a potential threat to currently available antibiotic treatments. Since KPC-producing bacteria may be difficult to detect, based on routine antibiotic susceptibility testing, they may cause problems in infection control measures. Another common β-lactamase family with carbapenemase properties is Guiana extended spectrum β-lactamase (GES) which is also particularly difficult to detect based on routine antibiotic susceptibility testing.
Large reservoir of carbapenem resistance genes in environmental species combined with increasing carbapenem use provoke the risk of emergence of rare or new carbapenemase genes, which may remain undetected. On the other hand carbapenem resistance may be caused by reversible mechanism as described above. Therefore, there is a need for improved methods for detecting carbapenemase genes causing carbapenem resistant bacteria in biological samples. Traditional biochemical methods are slow and unspesific and thus early detection of these strains requires new molecular methods.